Gaseous fuel powered engines and engines that operate on multiple different fuels are used in a variety of applications. Fuels for diesel engines of motor vehicles, such as diesel, biodiesel or gas-to-liquid fuel, i.e. liquid fuel obtained from natural gas, have very different fuel qualities. In particular, the ignitability of the fuel, which is important for the combustion in the cylinders of diesel engines and is usually expressed as the cetane index CCI or the cetane number, can vary considerably for different fuels. Even within the same types of fuel, combustion characteristics of the fuel such as the cetane index can vary widely.
An example of an internal combustion engine that can be reconfigured to operate with any given fuel from a range of combustible fuels is shown in U.S. Pat. No. 6,947,830 to Froloff et al. (“the '830 patent”). The '830 patent discloses a programmable computer system for an internal combustion engine configured to receive and process fuel combustion characteristic signals and data from various combustion events using different ignition methods. Detonation signals are processed from those combustion events to determine the fuel ignition method that will result in maximum power with allowable engine wear for a given fuel. Although the '830 patent purports to have the flexibility to run on a wide variety of fuels, a great deal of complexity of design and control is required in order to accommodate a variety of different ignition modes including spark ignition, homogeneous charge compression ignition, compression ignition, and combinations of the different ignition modes. Tests must be administered at engine start such that the engine is essentially controlled to act as a laboratory for a period of time in order to determine the least engine damaging ignition method to use that will also yield the highest power output for a particular fuel. These required test periods and reconfiguration of the engine to accommodate different modes of ignition may increase operating costs and reduce the ability of the engine to adjust quickly to different qualities of fuel that may be obtained at each refueling.
The wide range of different types of fuel and quality of the fuel that may be used by single fuel or multiple fuel engines makes it prohibitively expensive to test and verify an engine for this entire range of fuels. The different combustion characteristics of different types of fuel, and even for the same type of fuel obtained from different sources, creates a need for control systems that are able to automatically adjust for different fuels having different combustion characteristics while optimizing engine performance.
The disclosed system is directed to overcoming one or more of the problems set forth above and/or other problems with existing technologies.